The existence of tumor neoantigens in experimental animal tumors has been known for many years. There has been increasing evidence that human cancers, too, express tumor neoantigens that are recognized by humoral and cellular reactions of the host to the cancer cell or its products, in in vitro assays. See generally Shuster et al., Prog. Exp. Tumor Res., 25 89 (1980). This organ-specific neoantigen is shared by all cancers arising from the organ, so that patients with similar cancers will respond to each others cancer neoantigen.
It seems that human cancers may stimulate the hosts' immunologic response. Some prostatic carcinoma patients, for example, respond with a delayed cutaneous hypersensitivity reaction to injected tumor extract of the same histogenesis. Cell mediated cytotoxicity to the cancer was shown to exist in patients with prostatic carcinoma, especially those with stage B lesions.
With the discovery of the phenomenon of leucocyte adherence inhibition (LAI) a comparatively simple in vitro technique for measuring the hosts' antitumor immune response became available. See for example U.S. Pat. No. 3,999,944, issued Dec. 28, 1976 which describes the tube LAI assay for detection of the presence or absence of breast cancer in subjects. The extensions of the tube LAI to other tumor disease states is described in U.S. patent Ser. No. 68,378, filed Aug. 21, 1979, inventors Marti et al. Specific tumors disclosed include malignant melanoma, bladder carcinoma, ovarian cancer and cervical cancer.
The LAI assay is based on the observation that leucocytes from patients with cancer after being incubated in vitro with extracts of cancer tissue of the same organ and histogenesis, lose their former ability to adhere to glass, by binding to the tumor antigen.
One of the limitations of the LAI assay was the fact that substantial percentages of advanced cancer patients with various types of cancers do not have a measurable antitumor response and thus produce a false negative in the test. This fact limits the practical utility of the LAI in providing a broad scale clinical assay for cancer.
Failure of substantial numbers of cancer patients to express an antitumor immune response is particularly exemplified by the situation with prostatic carcinoma althought it can also be documented with breast, lung, stomach, pancreas, colon, bladder and melanoma cancers.
It has been found, for example, that relatively few patients (14%) with prostatic carcinoma had a measurable antitumor response. However, their tube LAI-positive responses were stastically greater than control subjects (1.5%) with or without benign prostatic hyperplasia (BPH).
The tube LAI procedure has also been previously described in detail by Grosser and Thomson, Cancer Res., 35 2571 (1975). In brief outline the procedure utilizes samples each containing B 0.1 ml of a peripheral blood leucocyte suspension (1.times.10.sup.7 cells/ml) which are incubated with either specific or nonspecific tumor antigen extracts (.about.100 .mu.g in 0.1 ml). The tubes are incubated horizontally for 2 hours at 37.degree. C. in a 5% CO.sub.2 humidified atmosphere. After 2 hours, the tubes are carefully placed vertically, and a sample of the non-adherent cells are counted by image analysis driven by computerized-linked instruments. The difference in non-adherent cells in the presence of cancer and a control tumor extract is expressed as a nonadherence index (NAI): ##EQU1##
Based on clinical experience with the assay it was determined that NAI's of 30 or greater are considered positive since greater than 95% of the patients without the specific cancer had NAI's of 30 or less.
The necessity in the above methodology that the nonadherent cells be counted by an automated computer linked counter is a further obstacle to the methodology becoming a widely accepted procedure since the cost of such instrumentation is prohibitive for most laboratories and requires the services of a highly trained technician; another expensive, acceptance limiting burden on the methodology.